NAR HPR Rocket Design & Aerodynamics 5

Question 1

What is 'corrective moment' in the context of rocket stability?

Accepted Answer

The restoring torque generated about the CG when the rocket flies at a non-zero angle of attack

Answer

When a rocket angles into the airflow, fins generate a normal force aft of CG that creates a torque rotating the nose back toward the velocity vector.

Question 2

For a given motor, how does increasing the rocket's dry mass (while keeping motor the same) affect the off-the-rod velocity?

Accepted Answer

Decreases off-the-rod velocity because greater mass results in lower acceleration for the same thrust

Answer

F=ma means that for constant thrust F, increasing mass m reduces acceleration a, resulting in a slower velocity when the rocket leaves the launch rod.

Question 3

What is the primary aerodynamic risk of a very over-stable rocket (e.g., 4+ calibers margin)?

Accepted Answer

Extreme weathercocking in any crosswind, causing significant horizontal range deviation

Answer

An over-stable rocket aggressively turns into even small crosswinds (weathercocks), which can cause it to fly nearly horizontally and land far from the launch site.

Question 4

Which statement about 'through-the-wall' (TTW) fin construction is correct?

Accepted Answer

TTW fin tabs pass through slots in the body tube and bond directly to the motor mount tube for superior strength

Answer

TTW construction routes fin tabs through the body tube wall to bond to the motor mount tube, creating a structurally superior joint that resists fin-shear loads under high dynamic pressure.

Question 5

During coast phase (after motor burnout), which statement best describes the rocket's aerodynamic behavior?

Accepted Answer

Fins continue to provide stabilizing restoring moments as long as the rocket has forward velocity

Answer

After burnout, the rocket continues to fly aerodynamically; fins still generate corrective moments proportional to dynamic pressure as long as velocity is positive.

(NAR HPR) NAR High-Power Rocketry Certification Practice Test

(NAR HPR) NAR High-Power Rocketry Certification Practice Test

NAR HPR Rocket Design & Aerodynamics 5